The present invention relates to a method for monitoring the operation of a device for carrying out an automatic braking process and to the device for carrying out an automatic braking process comprising a solenoid valve actuator carrying out an automatic braking process, a switch for terminating the automatic braking process under specific switching conditions, a displacement sensor for detecting travel of a brake pedal, a control device for controlling the automatic braking process and a test control device.
DE 42 08 496 C1 shows a partial-vacuum brake booster which has a solenoid valve for venting the pedal-side chamber in order to produce a higher brake pressure than results from the position of the brake pedal. Arranged on the brake pedal is, on one hand, a displacement sensor which detects the position of the brake pedal and, on the other hand, a switch which is actuated at least when the brake is released by the driver.
In this known device, the presence of operational faults of the device for carrying out an automatic braking process is not monitored. As a result, faults may occur which prevent automatic braking processes from being carried out in an operationally reliable way.
An object of the present invention is to provide a monitoring method for an automatic braking device to detect faults which could prevent an automatic braking process from being reliably carried out.
This object has been achieved according to the present invention by providing a method in which monitoring takes place by way of a test control device with a brief actuating of the solenoid valve by the test control device taking place under prescribed vehicle states, determining at least whether switching current of the solenoid actuator valve lies within prescribed limit values and via the displacement sensor, whether a pedal travel has occurred which corresponds to the pedal travel caused by the automatic braking process as criteria as to whether or not an operational fault of the automatic braking process has occurred, and if the determined criteria are not fulfilled the presence of an operational fault in the device for carrying out an automatic braking process is detected and appropriate intervention in the automatic braking process occurs.
The operational testing takes place by an automatic braking process which only lasts briefly and is not triggered by the control device of the automatic braking process but rather by a test control device. "Brief actuation" is used here in the sense of an actuation about a few tenths of a second, preferably only in the order of magnitude of approximately 50 ms. The actuation can take place during different travel states which are specified in the test control device. If it is detected here that the current through the solenoid valve is not within prescribed limit values or that a pedal travel which results from the actuation is not determined at the brake pedal, the presence of an operational fault of the device is concluded.
The actuation of the solenoid valve by the test control device can be carried out when the ignition of the vehicle is switched on, after the engine starts up and when the brake pedal is not being actuated for the first time after starting up. In addition, in the case of an operational fault the execution of an automatic braking process is prevented and the driver is informed of this via a display. Furthermore, other criteria are also presented which are used to test the operation of the device for carrying out an automatic braking process.